#!/usr/bin/perl
use strict;use warnings;

my $string = $ARGV[0];
my $test = $string;
my @illegal = qw(\ * ?);
my @legal = qw(bs a q);
my $c = 0;
foreach my $val (@illegal) {
    $test =~ s/\Q$val\E/[$legal[$c]]/g;
    $c++;
}
print $test."\n";

##</code><code>##

$ perl ./qt.pl 'a\\b\\c\d\\\\e'
a[bs][bs]b[bs][bs]c[bs]d[bs][bs][bs][bs]e
$ perl ./qt.pl 'foo*bar\eleven?three'
foo[a]bar[bs]eleven[q]three
$